Bacillus anthracis (B. anthracis or anthrax) remains a health threat for the developed world. Both lethal and edema toxin (LT and ET respectively) contribute to the pathogenesis of organ injury and lethality during anthrax infection. Understanding the mechanisms underlying the toxins pathogenic effects will be important for improving the outcome with this lethal infection. In vitro findings do suggest that each toxin can produce endothelial injury and loss of vascular integrity and increased permeability. Although never tested in the lung, increased endothelial permeability with the toxins could result in extravasation of fluid, reductions in oxygen transfer and lung compliance, and increased pulmonary vascular resistance. To investigate these possibilities, the present study will employ an isolated perfused rat lung model to examine whether LT or ET does cause pulmonary endothelial injury and increased pulmonary vascular permeability. This ex vivo model will allow a direct measure of changing lung weight over time, which is required to calculate a lung permeability coefficient. Determining whether either toxin alters lung permeability will improve our understanding of the pathogenesis and management of anthrax associated lung injury clinically. This study will be done in two parts. In the first part (Part 1), an isolated perfused rat lung model will be developed and the models ability to measure changes in endothelial permeability, oxygenation, compliance and vascular resistance tested with lungs isolated from healthy rats. As a positive control, Part 1 will include experiments in lungs challenged with thromboxane A2, a mediator known to increase lung endothelial permeability. In the second part (Part 2), lungs will be challenged with LT or ET introduced into the isolated lungs perfusion circuit and lung function will be measured. Some experiments in this part of the study will also include the use of Raxibacumab, a monoclonal antibody that inhibits host cell uptake of LT and ET, and adefovir, an intracellular inhibitor of ET, to further explore mechanisms underlying these toxins pathogenic effects. The functional parameters tested in Part 2 will include permeability, oxygenation, compliance and vascular resistance. Some lungs from Part 2 will be sent for histology and examination by electron microscopy. This study is ongoing.